The general problem of measuring flow rates and pressures of flowing fluids and fluid-like substances occurs in a wide variety of circumstances. Methods of measuring flow rates in a pipe often involve insertion of a probe or diversion of a portion of the flowing fluid. Such methods of measuring flow rate may involve undesirable disturbances of the flow and/or possible flow contamination. In traditional installations, where a pressure probe is offset from the flow, the added volume may entrap the material flowing in the line and present additional problems, such as clogging or bacteria growth.
In a particular exemplary flow measurement problem, that of measuring the pressure of slurries such as liquid concrete flowing in a tube, one method of isolating the slurry flow from the pressure transducer is to inject grease into a fluid line running from the tube to the pressure transducer while the measurement is being made. This intervening grease blocks concrete from reaching the pressure transducer, transmits pressure to the pressure transducer, and prevents damage to the pressure transducer. However, such a method is not suitable for continuous pressure measurement since grease must be injected before and during measurement. Some of the grease may be picked up by the flowing slurry, whereby such a method may introduce grease as an impurity to the slurry flow. Such an impurity may be unacceptable, whether the slurry is a flow of concrete, foodstuffs, or some other material.
Another method of measuring pressure in slurry flows involves measuring pressure of a sensing fluid in an isolated annular region. Between the sensing fluid and the slurry flow is an elastomeric cylinder which is to deform and thereby to transmit pressure from the slurry flow to the sensing fluid. An example of such a system is shown in U.S. Pat. No. 4,218,926, issued to DeVisser, entitled “Isolating Pressure Sensor.” Such systems have the disadvantages of being complicated and costly, as well as using an elastomeric material such as Buna-N, which may be unsuitable for contact with a corrosive or abrasive fluid or slurry.
In addition to slurries, it will be appreciated that there are many other fluids that may cause damage to a pressure transducer that is exposed to them. Examples of such fluids and fluid-like mixtures are corrosive materials and slurries or other mixtures containing abrasive materials.
From the foregoing general discussion and particular example, it may be seen that a need exists for an improved, inexpensive, and/or durable means of continuously measuring pressure and/or flow rate in flowing fluids.